THE TEMPORAL ARCHES OF THE REPTILIA. 



i8s 



the skull wall, the squamosal taking its function as an articula- 

 ting bone for the lower jaw. I see no urgent reason for insisting 

 that a vestige of it must yet be present in the eutherian skull, 

 either as a part of the zygomatic arch, or in a totally different 

 function as one of the ear bones. We are quite sure that some 

 of the bones of the reptilian skull are not present in the mam- 

 malian skull, why may not the quadrate be one of them ? 

 There seems to be an idea that bones of the reptilian skull can 

 only become lost by their union with contiguous bones, their 

 ossific centers finally disappearing. But I am skeptical of this. 

 We know that the quadratojugal is not present in the Squamata ; 

 that the ' prosquamosal ' of the arched lizards is not present in 



FIG. 1 6. Cimoliasanrus, original. 



the amphisbaenians or snakes ; that the epipterygoid is also wholly 

 wanting in some of the lizards, as well as other bones. Must 

 we insist that their loss has always been by fusion and loss of 

 ossific center? Must we insist that the lachrymal bone is always 

 present in the turtles, snakes and Sphenodon ; that the jugal is 

 still a part of the postorbital or maxilla of the snakes ; that the 

 prevomers still remain as a part of some other bones in the 

 eutherian mammals ; that the splenial and coronoid still remain 

 in the mammalian mandible ? 



Turning now to the double-barred or diapsid forms, it is a 

 question which of the two vacuities appeared first, or whether 

 they did not appear together. In Ichthyosaurus and Aetosaurus 

 we have a single vacuity, but the relations of both these forms 

 are so evident with the early rhynchocephaloid reptiles that 



